diff options
Diffstat (limited to 'doc/src/FAQ/FAQ_DEV.html')
| -rw-r--r-- | doc/src/FAQ/FAQ_DEV.html | 969 |
1 files changed, 505 insertions, 464 deletions
diff --git a/doc/src/FAQ/FAQ_DEV.html b/doc/src/FAQ/FAQ_DEV.html index 3c1433d345b..792446a1ac4 100644 --- a/doc/src/FAQ/FAQ_DEV.html +++ b/doc/src/FAQ/FAQ_DEV.html @@ -1,213 +1,229 @@ -<HTML> -<HEAD> -<TITLE>PostgreSQL Developers FAQ</title> -</HEAD> -<BODY BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#FF0000" VLINK="#A00000" ALINK="#0000FF"> -<H1> -Developer's Frequently Asked Questions (FAQ) for PostgreSQL -</H1> -<P> -Last updated: Fri Jun 9 21:54:54 EDT 2000 -<P> -Current maintainer: Bruce Momjian (<a -href="mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</a>)<BR> -<P> -The most recent version of this document can be viewed at -the postgreSQL Web site, <a -href="http://PostgreSQL.org">http://PostgreSQL.org</a>. -<P> -<HR> -<P> - -<CENTER><H2>Questions</H2></CENTER> -<a href="#1">1</a>) What tools are available for developers?<BR> -<a href="#2">2</a>) What books are good for developers?<BR> -<a href="#3">3</a>) Why do we use <I>palloc</I>() and <I>pfree</I>() to allocate memory?<BR> -<a href="#4">4</a>) Why do we use <I>Node</I> and <I>List</I> to -make data structures?<BR> -<a href="#5">5</a>) How do I add a feature or fix a bug?<BR> -<a href="#6">6</a>) How do I download/update the current source tree?<BR> -<a href="#7">7</a>) How do I test my changes?<BR> -<a href="#7">7</a>) I just added a field to a structure. What else -should I do?<BR> -<a href="#8">8</a>) Why are table, column, type, function, view -names sometimes referenced as <I>Name</I> or <I>NameData,</I> and -sometimes as <I>char *?</I><BR> -<a href="#9">9</a>) How do I efficiently access information in -tables from the backend code?<BR> -<a href="#10">10</a>) What is elog()?<BR> -<a href="#11">11</a>) What is configure all about?<BR> -<a href="#12">12</a>) How do I add a new port?<BR> -<a href="#13">13</a>) What is CommandCounterIncrement()?<BR> -<BR> -<HR> - -<H3><a -name="1">1</a>) What tools are available for developers?</H3><P> - -Aside from the User documentation mentioned in the regular FAQ, there -are several development tools available. First, all the files in the -<I>/tools</I> directory are designed for developers. +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2//EN"> +<HTML> + <HEAD> + <META name="generator" content="HTML Tidy, see www.w3.org"> + + <TITLE>PostgreSQL Developers FAQ</TITLE> + </HEAD> + + <BODY bgcolor="#FFFFFF" text="#000000" link="#FF0000" vlink="#A00000" + alink="#0000FF"> + <H1>Developer's Frequently Asked Questions (FAQ) for + PostgreSQL</H1> + + <P>Last updated: Fri Jun 9 21:54:54 EDT 2000</P> + + <P>Current maintainer: Bruce Momjian (<A href= + "mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR> + </P> + + <P>The most recent version of this document can be viewed at the + postgreSQL Web site, <A href= + "http://PostgreSQL.org">http://PostgreSQL.org</A>.<BR> + </P> + <HR> + <BR> + + + <CENTER> + <H2>Questions</H2> + </CENTER> + <A href="#1">1</A>) What tools are available for developers?<BR> + <A href="#2">2</A>) What books are good for developers?<BR> + <A href="#3">3</A>) Why do we use <I>palloc</I>() and + <I>pfree</I>() to allocate memory?<BR> + <A href="#4">4</A>) Why do we use <I>Node</I> and <I>List</I> to + make data structures?<BR> + <A href="#5">5</A>) How do I add a feature or fix a bug?<BR> + <A href="#6">6</A>) How do I download/update the current source + tree?<BR> + <A href="#7">7</A>) How do I test my changes?<BR> + <A href="#7">7</A>) I just added a field to a structure. What else + should I do?<BR> + <A href="#8">8</A>) Why are table, column, type, function, view + names sometimes referenced as <I>Name</I> or <I>NameData,</I> and + sometimes as <I>char *?</I><BR> + <A href="#9">9</A>) How do I efficiently access information in + tables from the backend code?<BR> + <A href="#10">10</A>) What is elog()?<BR> + <A href="#11">11</A>) What is configure all about?<BR> + <A href="#12">12</A>) How do I add a new port?<BR> + <A href="#13">13</A>) What is CommandCounterIncrement()?<BR> + <A href="#14">13</A>) Why don't we use threads in the backend?<BR> + <BR> + + <HR> + + <H3><A name="1">1</A>) What tools are available for + developers?</H3> + + <P>Aside from the User documentation mentioned in the regular FAQ, + there are several development tools available. First, all the files + in the <I>/tools</I> directory are designed for developers.</P> <PRE> - RELEASE_CHANGES changes we have to make for each release - SQL_keywords standard SQL'92 keywords - backend description/flowchart of the backend directories - ccsym find standard defines made by your compiler - entab converts tabs to spaces, used by pgindent - find_static finds functions that could be made static - find_typedef get a list of typedefs in the source code - make_ctags make vi 'tags' file in each directory - make_diff make *.orig and diffs of source - make_etags make emacs 'etags' files - make_keywords.README make comparison of our keywords and SQL'92 - make_mkid make mkid ID files - mkldexport create AIX exports file - pgindent indents C source files - pginclude scripts for adding/removing include files - unused_oids in pgsql/src/include/catalog + RELEASE_CHANGES changes we have to make for each release + SQL_keywords standard SQL'92 keywords + backend description/flowchart of the backend directories + ccsym find standard defines made by your compiler + entab converts tabs to spaces, used by pgindent + find_static finds functions that could be made static + find_typedef get a list of typedefs in the source code + make_ctags make vi 'tags' file in each directory + make_diff make *.orig and diffs of source + make_etags make emacs 'etags' files + make_keywords.README make comparison of our keywords and SQL'92 + make_mkid make mkid ID files + mkldexport create AIX exports file + pgindent indents C source files + pginclude scripts for adding/removing include files + unused_oids in pgsql/src/include/catalog </PRE> + Let me note some of these. If you point your browser at the + <I>file:/usr/local/src/pgsql/src/tools/backend/index.html</I> + directory, you will see few paragraphs describing the data flow, + the backend components in a flow chart, and a description of the + shared memory area. You can click on any flowchart box to see a + description. If you then click on the directory name, you will be + taken to the source directory, to browse the actual source code + behind it. We also have several README files in some source + directories to describe the function of the module. The browser + will display these when you enter the directory also. The + <I>tools/backend</I> directory is also contained on our web page + under the title <I>How PostgreSQL Processes a Query.</I> + + <P>Second, you really should have an editor that can handle tags, + so you can tag a function call to see the function definition, and + then tag inside that function to see an even lower-level function, + and then back out twice to return to the original function. Most + editors support this via <I>tags</I> or <I>etags</I> files.</P> + + <P>Third, you need to get <I>id-utils</I> from:</P> +<PRE> + <A href= +"ftp://alpha.gnu.org/gnu/id-utils-3.2d.tar.gz">ftp://alpha.gnu.org/gnu/id-utils-3.2d.tar.gz</A> + <A href= +"ftp://tug.org/gnu/id-utils-3.2d.tar.gz">ftp://tug.org/gnu/id-utils-3.2d.tar.gz</A> + <A href= +"ftp://ftp.enst.fr/pub/gnu/gnits/id-utils-3.2d.tar.gz">ftp://ftp.enst.fr/pub/gnu/gnits/id-utils-3.2d.tar.gz</A> +</PRE> + By running <I>tools/make_mkid</I>, an archive of source symbols can + be created that can be rapidly queried like <I>grep</I> or edited. + Others prefer <I>glimpse.</I> -Let me note some of these. If you point your browser at the -<I>file:/usr/local/src/pgsql/src/tools/backend/index.html</I> directory, -you will see few paragraphs describing the data flow, the backend -components in a flow chart, and a description of the shared memory area. -You can click on any flowchart box to see a description. If you then -click on the directory name, you will be taken to the source directory, -to browse the actual source code behind it. We also have several README -files in some source directories to describe the function of the module. - The browser will display these when you enter the directory also. The -<I>tools/backend</I> directory is also contained on our web page under -the title <I>How PostgreSQL Processes a Query.</I><P> - - -Second, you really should have an editor that can handle tags, so you -can tag a function call to see the function definition, and then tag -inside that function to see an even lower-level function, and then back -out twice to return to the original function. Most editors support this -via <I>tags</I> or <I>etags</I> files.<P> - - -Third, you need to get <I>id-utils</I> from: -<pre> - <a href="ftp://alpha.gnu.org/gnu/id-utils-3.2d.tar.gz">ftp://alpha.gnu.org/gnu/id-utils-3.2d.tar.gz</a> - <a href="ftp://tug.org/gnu/id-utils-3.2d.tar.gz">ftp://tug.org/gnu/id-utils-3.2d.tar.gz</a> - <a href="ftp://ftp.enst.fr/pub/gnu/gnits/id-utils-3.2d.tar.gz">ftp://ftp.enst.fr/pub/gnu/gnits/id-utils-3.2d.tar.gz</a> -</pre> - -By running <I>tools/make_mkid</I>, an archive of source symbols can be -created that can be rapidly queried like <I>grep</I> or edited. Others -prefer <I>glimpse.</I><P> - - -<I>make_diff</I> has tools to create patch diff files that can be -applied to the distribution.<P> - + <P><I>make_diff</I> has tools to create patch diff files that can + be applied to the distribution.</P> -Our standard format is to indent each code level with one tab, where -each tab is four spaces. You will need to set your editor to display -tabs as four spaces: -<BR> + <P>Our standard format is to indent each code level with one tab, + where each tab is four spaces. You will need to set your editor to + display tabs as four spaces:<BR> + </P> <PRE> - vi in ~/.exrc: - set tabstop=4 - set sw=4 - more: - more -x4 - less: - less -x4 - emacs: - M-x set-variable tab-width - or - ; Cmd to set tab stops &etc for working with PostgreSQL code + vi in ~/.exrc: + set tabstop=4 + set sw=4 + more: + more -x4 + less: + less -x4 + emacs: + M-x set-variable tab-width + or + ; Cmd to set tab stops & indenting for working with PostgreSQL code (c-add-style "pgsql" - '("bsd" + '("bsd" (indent-tabs-mode . t) (c-basic-offset . 4) (tab-width . 4) - (c-offsets-alist . + (c-offsets-alist . ((case-label . +)))) t) ; t = set this mode on - and add this to your autoload list (modify file path in macro): - - (setq auto-mode-alist - (cons '("\\`/usr/local/src/pgsql/.*\\.[chyl]\\'" . pgsql-c-mode) - auto-mode-alist)) - or - /* - * Local variables: - * tab-width: 4 - * c-indent-level: 4 - * c-basic-offset: 4 - * End: - */ + and add this to your autoload list (modify file path in macro): + + (setq auto-mode-alist + (cons '("\\`/usr/local/src/pgsql/.*\\.[chyl]\\'" . pgsql-c-mode) + auto-mode-alist)) + or + /* + * Local variables: + * tab-width: 4 + * c-indent-level: 4 + * c-basic-offset: 4 + * End: + */ </PRE> -<BR> -<I>pgindent</I> will the format code by specifying -flags to your operating system's utility <I>indent.</I><P> -<I>pgindent</I> is run on all source files just before each beta test -period. It auto-formats all source files to make them consistent. -Comment blocks that need specific line breaks should be formatted as -<I>block comments,</I> where the comment starts as -<CODE>/*------</CODE>. These comments will not be reformatted in any -way. - -<I>pginclude</I> contains scripts used to add needed #include's to -include files, and removed unneeded #include's. - -When adding system types, you will need to assign oids to them. -There is also a script called <I>unused_oids</I> in -<I>pgsql/src/include/catalog</I> that shows the unused oids. - -<H3><a name="2">2</a>) What books are good for developers?</H3><P> - -I have four good books, <I>An Introduction to Database Systems,</I> by -C.J. Date, Addison, Wesley, <I>A Guide to the SQL Standard,</I> by C.J. -Date, et. al, Addison, Wesley, <I>Fundamentals of Database Systems,</I> -by Elmasri and Navathe, and <I>Transaction Processing,</I> by Jim Gray, -Morgan, Kaufmann<P> - -There is also a database performance site, with a handbook on-line -written by Jim Gray at <A -HREF="http://www.benchmarkresources.com">http://www.benchmarkresources.com.</A> - - - -<H3><a name="3">3</a>) Why do we use <I>palloc</I>() and <I>pfree</I>() -to allocate memory?</H3><P> - -<I>palloc()</I> and <I>pfree()</I> are used in place of malloc() and -free() because we automatically free all memory allocated when a -transaction completes. This makes it easier to make sure we free memory -that gets allocated in one place, but only freed much later. There are -several contexts that memory can be allocated in, and this controls when -the allocated memory is automatically freed by the backend.<P> - - -<H3><a name="4">4</a>) Why do we use <I>Node</I> and <I>List</I> to -make data structures?</H3><P> - -We do this because this allows a consistent way to pass data inside the -backend in a flexible way. Every node has a <I>NodeTag</I> which -specifies what type of data is inside the Node. <I>Lists</I> are groups -of <I>Nodes chained together as a forward-linked list.</I><P> -Here are some of the <I>List</I> manipulation commands: -<BLOCKQUOTE> -<DL> -<DT>lfirst(i) -<DD>return the data at list element <I>i.</I> -<DT>lnext(i) -<DD>return the next list element after <I>i.</I> -<DT>foreach(i, list) -<DD>loop through <I>list,</I> assigning each list element to <I>i.</I> -It is important to note that <I>i</I> is a List *, not the data in the -<I>List</I> element. You need to use <I>lfirst(i)</I> to get at the data. -Here is a typical code snipped that loops through a List containing -<I>Var *'s</I> and processes each one: + <BR> + <I>pgindent</I> will the format code by specifying flags to your + operating system's utility <I>indent.</I> + + <P><I>pgindent</I> is run on all source files just before each beta + test period. It auto-formats all source files to make them + consistent. Comment blocks that need specific line breaks should be + formatted as <I>block comments,</I> where the comment starts as + <CODE>/*------</CODE>. These comments will not be reformatted in + any way. <I>pginclude</I> contains scripts used to add needed + #include's to include files, and removed unneeded #include's. When + adding system types, you will need to assign oids to them. There is + also a script called <I>unused_oids</I> in + <I>pgsql/src/include/catalog</I> that shows the unused oids.</P> + + <H3><A name="2">2</A>) What books are good for developers?</H3> + + <P>I have four good books, <I>An Introduction to Database + Systems,</I> by C.J. Date, Addison, Wesley, <I>A Guide to the SQL + Standard,</I> by C.J. Date, et. al, Addison, Wesley, + <I>Fundamentals of Database Systems,</I> by Elmasri and Navathe, + and <I>Transaction Processing,</I> by Jim Gray, Morgan, + Kaufmann</P> + + <P>There is also a database performance site, with a handbook + on-line written by Jim Gray at <A href= + "http://www.benchmarkresources.com">http://www.benchmarkresources.com.</A></P> + + <H3><A name="3">3</A>) Why do we use <I>palloc</I>() and + <I>pfree</I>() to allocate memory?</H3> + + <P><I>palloc()</I> and <I>pfree()</I> are used in place of malloc() + and free() because we automatically free all memory allocated when + a transaction completes. This makes it easier to make sure we free + memory that gets allocated in one place, but only freed much later. + There are several contexts that memory can be allocated in, and + this controls when the allocated memory is automatically freed by + the backend.</P> + + <H3><A name="4">4</A>) Why do we use <I>Node</I> and <I>List</I> to + make data structures?</H3> + + <P>We do this because this allows a consistent way to pass data + inside the backend in a flexible way. Every node has a + <I>NodeTag</I> which specifies what type of data is inside the + Node. <I>Lists</I> are groups of <I>Nodes chained together as a + forward-linked list.</I></P> + + <P>Here are some of the <I>List</I> manipulation commands:</P> + + <BLOCKQUOTE> + <DL> + <DT>lfirst(i)</DT> + + <DD>return the data at list element <I>i.</I></DD> + + <DT>lnext(i)</DT> + + <DD>return the next list element after <I>i.</I></DD> + + <DT>foreach(i, list)</DT> + + <DD> + loop through <I>list,</I> assigning each list element to + <I>i.</I> It is important to note that <I>i</I> is a List *, + not the data in the <I>List</I> element. You need to use + <I>lfirst(i)</I> to get at the data. Here is a typical code + snipped that loops through a List containing <I>Var *'s</I> + and processes each one: <PRE> -<CODE> - List *i, *list; +<CODE>List *i, *list; foreach(i, list) { @@ -216,282 +232,307 @@ Here is a typical code snipped that loops through a List containing /* process var here */ } </CODE> -</PRE> -<DT>lcons(node, list) -<DD>add <I>node</I> to the front of <I>list,</I> or create a new list with -<I>node</I> if <I>list</I> is <I>NIL.</I> -<DT>lappend(list, node) -<DD>add <I>node</I> to the end of <I>list.</I> This is more expensive -that lcons. -<DT>nconc(list1, list2) -<DD>Concat <I>list2</I> on to the end of <I>list1.</I> -<DT>length(list) -<DD>return the length of the <I>list.</I> -<DT>nth(i, list) -<DD>return the <I>i</I>'th element in <I>list.</I> -<DT>lconsi, ... -<DD>There are integer versions of these: <I>lconsi, lappendi, nthi.</I> -<I>List's</I> containing integers instead of Node pointers are used to -hold list of relation object id's and other integer quantities. -</DL> -</BLOCKQUOTE> -You can print nodes easily inside <I>gdb.</I> First, to disable -output truncation when you use the gdb <I>print</I> command: +</PRE> + </DD> + + <DT>lcons(node, list)</DT> + + <DD>add <I>node</I> to the front of <I>list,</I> or create a + new list with <I>node</I> if <I>list</I> is <I>NIL.</I></DD> + + <DT>lappend(list, node)</DT> + + <DD>add <I>node</I> to the end of <I>list.</I> This is more + expensive that lcons.</DD> + + <DT>nconc(list1, list2)</DT> + + <DD>Concat <I>list2</I> on to the end of <I>list1.</I></DD> + + <DT>length(list)</DT> + + <DD>return the length of the <I>list.</I></DD> + + <DT>nth(i, list)</DT> + + <DD>return the <I>i</I>'th element in <I>list.</I></DD> + + <DT>lconsi, ...</DT> + + <DD>There are integer versions of these: <I>lconsi, lappendi, + nthi.</I> <I>List's</I> containing integers instead of Node + pointers are used to hold list of relation object id's and + other integer quantities.</DD> + </DL> + </BLOCKQUOTE> + You can print nodes easily inside <I>gdb.</I> First, to disable + output truncation when you use the gdb <I>print</I> command: +<PRE> +<CODE>(gdb) set print elements 0 +</CODE> +</PRE> + Instead of printing values in gdb format, you can use the next two + commands to print out List, Node, and structure contents in a + verbose format that is easier to understand. List's are unrolled + into nodes, and nodes are printed in detail. The first prints in a + short format, and the second in a long format: <PRE> -<CODE> - (gdb) set print elements 0 +<CODE>(gdb) call print(any_pointer) + (gdb) call pprint(any_pointer) </CODE> </PRE> -Instead of printing values in gdb format, you can use the next two -commands to print out List, Node, and structure contents in a verbose -format that is easier to understand. List's are unrolled into nodes, -and nodes are printed in detail. The first prints in a short format, -and the second in a long format: + The output appears in the postmaster log file, or on your screen if + you are running a backend directly without a postmaster. + + <H3><A name="5">5</A>) How do I add a feature or fix a bug?</H3> + + <P>The source code is over 250,000 lines. Many problems/features + are isolated to one specific area of the code. Others require + knowledge of much of the source. If you are confused about where to + start, ask the hackers list, and they will be glad to assess the + complexity and give pointers on where to start.</P> + + <P>Another thing to keep in mind is that many fixes and features + can be added with surprisingly little code. I often start by adding + code, then looking at other areas in the code where similar things + are done, and by the time I am finished, the patch is quite small + and compact.</P> + + <P>When adding code, keep in mind that it should use the existing + facilities in the source, for performance reasons and for + simplicity. Often a review of existing code doing similar things is + helpful.</P> + + <H3><A name="6">6</A>) How do I download/update the current source + tree?</H3> + + <P>There are several ways to obtain the source tree. Occasional + developers can just get the most recent source tree snapshot from + ftp.postgresql.org. For regular developers, you can use CVS. CVS + allows you to download the source tree, then occasionally update + your copy of the source tree with any new changes. Using CVS, you + don't have to download the entire source each time, only the + changed files. Anonymous CVS does not allows developers to update + the remote source tree, though privileged developers can do this. + There is a CVS FAQ on our web site that describes how to use remote + CVS. You can also use CVSup, which has similarly functionality, and + is available from ftp.postgresql.org.</P> + + <P>To update the source tree, there are two ways. You can generate + a patch against your current source tree, perhaps using the + make_diff tools mentioned above, and send them to the patches list. + They will be reviewed, and applied in a timely manner. If the patch + is major, and we are in beta testing, the developers may wait for + the final release before applying your patches.</P> + + <P>For hard-core developers, Marc(scrappy@postgresql.org) will give + you a Unix shell account on postgresql.org, so you can use CVS to + update the main source tree, or you can ftp your files into your + account, patch, and cvs install the changes directly into the + source tree.</P> + + <H3><A name="6">6</A>) How do I test my changes?</H3> + + <P>First, use <I>psql</I> to make sure it is working as you expect. + Then run <I>src/test/regress</I> and get the output of + <I>src/test/regress/checkresults</I> with and without your changes, + to see that your patch does not change the regression test in + unexpected ways. This practice has saved me many times. The + regression tests test the code in ways I would never do, and has + caught many bugs in my patches. By finding the problems now, you + save yourself a lot of debugging later when things are broken, and + you can't figure out when it happened.</P> + + <H3><A name="7">7</A>) I just added a field to a structure. What + else should I do?</H3> + + <P>The structures passing around from the parser, rewrite, + optimizer, and executor require quite a bit of support. Most + structures have support routines in <I>src/backend/nodes</I> used + to create, copy, read, and output those structures. Make sure you + add support for your new field to these files. Find any other + places the structure may need code for your new field. <I>mkid</I> + is helpful with this (see above).</P> + + <H3><A name="8">8</A>) Why are table, column, type, function, view + names sometimes referenced as <I>Name</I> or <I>NameData,</I> and + sometimes as <I>char *?</I></H3> + + <P>Table, column, type, function, and view names are stored in + system tables in columns of type <I>Name.</I> Name is a + fixed-length, null-terminated type of <I>NAMEDATALEN</I> bytes. + (The default value for NAMEDATALEN is 32 bytes.)</P> <PRE> -<CODE> - (gdb) call print(any_pointer) - (gdb) call pprint(any_pointer) +<CODE>typedef struct nameData + { + char data[NAMEDATALEN]; + } NameData; + typedef NameData *Name; </CODE> </PRE> -The output appears in the postmaster log file, or on your screen if you -are running a backend directly without a postmaster. -<P> - -<H3><a name="5">5</a>) How do I add a feature or fix a bug?</H3><P> - -The source code is over 250,000 lines. Many problems/features are -isolated to one specific area of the code. Others require knowledge of -much of the source. If you are confused about where to start, ask the -hackers list, and they will be glad to assess the complexity and give -pointers on where to start.<P> - -Another thing to keep in mind is that many fixes and features can be -added with surprisingly little code. I often start by adding code, then -looking at other areas in the code where similar things are done, and by -the time I am finished, the patch is quite small and compact.<P> - -When adding code, keep in mind that it should use the existing -facilities in the source, for performance reasons and for simplicity. -Often a review of existing code doing similar things is helpful.<P> - - -<H3><a name="6">6</a>) How do I download/update the current source -tree?</H3><P> - - -There are several ways to obtain the source tree. Occasional developers -can just get the most recent source tree snapshot from -ftp.postgresql.org. For regular developers, you can use CVS. CVS -allows you to download the source tree, then occasionally update your -copy of the source tree with any new changes. Using CVS, you don't have -to download the entire source each time, only the changed files. -Anonymous CVS does not allows developers to update the remote source -tree, though privileged developers can do this. There is a CVS FAQ on -our web site that describes how to use remote CVS. You can also use -CVSup, which has similarly functionality, and is available from -ftp.postgresql.org.<P> - -To update the source tree, there are two ways. You can generate a patch -against your current source tree, perhaps using the make_diff tools -mentioned above, and send them to the patches list. They will be -reviewed, and applied in a timely manner. If the patch is major, and we -are in beta testing, the developers may wait for the final release -before applying your patches.<P> - -For hard-core developers, Marc(scrappy@postgresql.org) will give you a -Unix shell account on postgresql.org, so you can use CVS to update the -main source tree, or you can ftp your files into your account, patch, -and cvs install the changes directly into the source tree. <P> - -<H3><a name="6">6</a>) How do I test my changes?</H3><P> - -First, use <I>psql</I> to make sure it is working as you expect. Then -run <I>src/test/regress</I> and get the output of -<I>src/test/regress/checkresults</I> with and without your changes, to -see that your patch does not change the regression test in unexpected -ways. This practice has saved me many times. The regression tests test -the code in ways I would never do, and has caught many bugs in my -patches. By finding the problems now, you save yourself a lot of -debugging later when things are broken, and you can't figure out when it -happened.<P> - - -<H3><a name="7">7</a>) I just added a field to a structure. What else -should I do?</H3><P> - -The structures passing around from the parser, rewrite, optimizer, and -executor require quite a bit of support. Most structures have support -routines in <I>src/backend/nodes</I> used to create, copy, read, and output -those structures. Make sure you add support for your new field to these -files. Find any other places the structure may need code for your new -field. <I>mkid</I> is helpful with this (see above).<P> - - -<H3><a name="8">8</a>) Why are table, column, type, function, view -names sometimes referenced as <I>Name</I> or <I>NameData,</I> and -sometimes as <I>char *?</I></H3><P> - -Table, column, type, function, and view names are stored in system -tables in columns of type <I>Name.</I> Name is a fixed-length, -null-terminated type of <I>NAMEDATALEN</I> bytes. (The default value -for NAMEDATALEN is 32 bytes.) - -<PRE><CODE> - typedef struct nameData - { - char data[NAMEDATALEN]; - } NameData; - typedef NameData *Name; -</CODE></PRE> - -Table, column, type, function, and view names that come into the -backend via user queries are stored as variable-length, null-terminated -character strings.<P> - -Many functions are called with both types of names, ie. <I>heap_open().</I> -Because the Name type is null-terminated, it is safe to pass it to a -function expecting a char *. Because there are many cases where on-disk -names(Name) are compared to user-supplied names(char *), there are many -cases where Name and char * are used interchangeably.<P> - -<H3><a name="9">9</a>) How do I efficiently access information in -tables from the backend code?</H3><P> - -You first need to find the tuples(rows) you are interested in. There -are two ways. First, <I>SearchSysCache()</I> and related functions -allow you to query the system catalogs. This is the preferred way to -access system tables, because the first call to the cache loads the -needed rows, and future requests can return the results without -accessing the base table. The caches use system table indexes -to look up tuples. A list of available caches is located in -<I>src/backend/utils/cache/syscache.c.</I> -<I>src/backend/utils/cache/lsyscache.c</I> contains many column-specific -cache lookup functions.<P> - -The rows returned are cache-owned versions of the heap rows. Therefore, you -must not modify or delete the tuple returned by <I>SearchSysCache()</I>. What -you <I>should</I> do is release it with <I>ReleaseSysCache()</I> when you are -done using it; this informs the cache that it can discard that tuple if -necessary. If you neglect to call <I>ReleaseSysCache()</I>, then the cache -entry will remain locked in the cache until end of transaction, which is -tolerable but not very desirable.<P> - -If you can't use the system cache, you will need to retrieve the data -directly from the heap table, using the buffer cache that is shared by -all backends. The backend automatically takes care of loading the rows -into the buffer cache.<P> - -Open the table with <I>heap_open().</I> You can then start a table scan -with <I>heap_beginscan(),</I> then use <I>heap_getnext()</I> and -continue as long as <I>HeapTupleIsValid()</I> returns true. Then do a -<I>heap_endscan().</I> <I>Keys</I> can be assigned to the <I>scan.</I> -No indexes are used, so all rows are going to be compared to the keys, -and only the valid rows returned.<P> - -You can also use <I>heap_fetch()</I> to fetch rows by block -number/offset. While scans automatically lock/unlock rows from the -buffer cache, with <I>heap_fetch(),</I> you must pass a <I>Buffer</I> -pointer, and <I>ReleaseBuffer()</I> it when completed.<P> - -Once you have the row, you can get data that is common to all tuples, -like <I>t_self</I> and <I>t_oid,</I> by merely accessing the -<I>HeapTuple</I> structure entries. -If you need a table-specific column, you should take the HeapTuple -pointer, and use the <I>GETSTRUCT()</I> macro to access the -table-specific start of the tuple. You then cast the pointer as a -<I>Form_pg_proc</I> pointer if you are accessing the pg_proc table, or -<I>Form_pg_type</I> if you are accessing pg_type. You can then access -the columns by using a structure pointer: - + Table, column, type, function, and view names that come into the + backend via user queries are stored as variable-length, + null-terminated character strings. + + <P>Many functions are called with both types of names, ie. + <I>heap_open().</I> Because the Name type is null-terminated, it is + safe to pass it to a function expecting a char *. Because there are + many cases where on-disk names(Name) are compared to user-supplied + names(char *), there are many cases where Name and char * are used + interchangeably.</P> + + <H3><A name="9">9</A>) How do I efficiently access information in + tables from the backend code?</H3> + + <P>You first need to find the tuples(rows) you are interested in. + There are two ways. First, <I>SearchSysCache()</I> and related + functions allow you to query the system catalogs. This is the + preferred way to access system tables, because the first call to + the cache loads the needed rows, and future requests can return the + results without accessing the base table. The caches use system + table indexes to look up tuples. A list of available caches is + located in <I>src/backend/utils/cache/syscache.c.</I> + <I>src/backend/utils/cache/lsyscache.c</I> contains many + column-specific cache lookup functions.</P> + + <P>The rows returned are cache-owned versions of the heap rows. + Therefore, you must not modify or delete the tuple returned by + <I>SearchSysCache()</I>. What you <I>should</I> do is release it + with <I>ReleaseSysCache()</I> when you are done using it; this + informs the cache that it can discard that tuple if necessary. If + you neglect to call <I>ReleaseSysCache()</I>, then the cache entry + will remain locked in the cache until end of transaction, which is + tolerable but not very desirable.</P> + + <P>If you can't use the system cache, you will need to retrieve the + data directly from the heap table, using the buffer cache that is + shared by all backends. The backend automatically takes care of + loading the rows into the buffer cache.</P> + + <P>Open the table with <I>heap_open().</I> You can then start a + table scan with <I>heap_beginscan(),</I> then use + <I>heap_getnext()</I> and continue as long as + <I>HeapTupleIsValid()</I> returns true. Then do a + <I>heap_endscan().</I> <I>Keys</I> can be assigned to the + <I>scan.</I> No indexes are used, so all rows are going to be + compared to the keys, and only the valid rows returned.</P> + + <P>You can also use <I>heap_fetch()</I> to fetch rows by block + number/offset. While scans automatically lock/unlock rows from the + buffer cache, with <I>heap_fetch(),</I> you must pass a + <I>Buffer</I> pointer, and <I>ReleaseBuffer()</I> it when + completed.</P> + + <P>Once you have the row, you can get data that is common to all + tuples, like <I>t_self</I> and <I>t_oid,</I> by merely accessing + the <I>HeapTuple</I> structure entries. If you need a + table-specific column, you should take the HeapTuple pointer, and + use the <I>GETSTRUCT()</I> macro to access the table-specific start + of the tuple. You then cast the pointer as a <I>Form_pg_proc</I> + pointer if you are accessing the pg_proc table, or + <I>Form_pg_type</I> if you are accessing pg_type. You can then + access the columns by using a structure pointer:</P> <PRE> -<CODE> - ((Form_pg_class) GETSTRUCT(tuple))->relnatts +<CODE>((Form_pg_class) GETSTRUCT(tuple))->relnatts </CODE> </PRE> - -You must not directly change <I>live</I> tuples in this way. The best -way is to use <I>heap_modifytuple()</I> and pass it your original -tuple, and the values you want changed. It returns a palloc'ed -tuple, which you pass to <I>heap_replace().</I> - -You can delete tuples by passing the tuple's <I>t_self</I> to -<I>heap_destroy().</I> You use <I>t_self</I> for <I>heap_update()</I> too. - -Remember, tuples can be either system cache copies, which may go away after -you call <I>ReleaseSysCache()</I>, or read directly from disk buffers, which -go away when you <I>heap_getnext()</I>, <I>heap_endscan</I>, or -<I>ReleaseBuffer()</I>, in the <I>heap_fetch()</I> case. Or it may be a -palloc'ed tuple, that you must <I>pfree()</I> when finished. - -<H3><a name="10">10</a>) What is elog()?</H3><P> - -<I>elog()</I> is used to send messages to the front-end, and optionally -terminate the current query being processed. The first parameter is an -elog level of <I>NOTICE,</I> <I>DEBUG,</I> <I>ERROR,</I> or -<I>FATAL.</I> - -<I>NOTICE</I> prints on the user's terminal and the postmaster logs. -<I>DEBUG</I> prints only in the postmaster logs. <I>ERROR</I> prints in -both places, and terminates the current query, never returning from the call. -<I>FATAL</I> terminates the backend process. - -The remaining parameters of <I>elog</I> are a <I>printf</I>-style set of -parameters to print. - -<H3><a name="11">11</a>) What is configure all about?</H3><P> - -The files <I>configure</I> and <I>configure.in</I> are part of the -GNU <I>autoconf</I> package. Configure allows us to test for various -capabilities of the OS, and to set variables that can then be tested in -C programs and Makefiles. Autoconf is installed on the PostgreSQL main -server. To add options to configure, edit <I>configure.in,</I> and then -run <I>autoconf</I> to generate <I>configure.</I><P> - -When <I>configure</I> is run by the user, it tests various OS -capabilities, stores those in <I>config.status</I> and -<I>config.cache,</I> and modifies a list of <I>*.in</I> files. For -example, if there exists a <I>Makefile.in,</I> configure generates a -<I>Makefile</I> that contains substitutions for all @var@ parameters -found by configure.<P> - -When you need to edit files, make sure you don't waste time modifying -files generated by <I>configure.</I> Edit the <I>*.in</I> file, and -re-run <I>configure</I> to recreate the needed file. If you run <I>make -distclean</I> from the top-level source directory, all files derived by -configure are removed, so you see only the file contained in the source -distribution.<P> - -<H3><a name="12">12</a>) How do I add a new port?</H3><P> - -There are a variety of places that need to be modified to add a new -port. First, start in the <I>src/template</I> directory. Add an -appropriate entry for your OS. Also, use <I>src/config.guess</I> to add -your OS to <I>src/template/.similar.</I> You shouldn't match the OS -version exactly. The <I>configure</I> test will look for an exact OS -version number, and if not found, find a match without version number. -Edit <I>src/configure.in</I> to add your new OS. (See configure item -above.) You will need to run autoconf, or patch <I>src/configure</I> -too.<P> - -Then, check <I>src/include/port</I> and add your new OS file, with -appropriate values. Hopefully, there is already locking code in -<I>src/include/storage/s_lock.h</I> for your CPU. There is also a -<I>src/makefiles</I> directory for port-specific Makefile handling. -There is a <I>backend/port</I> directory if you need special files for -your OS.<P> - -<H3><a name="13">13</a>) What is CommandCounterIncrement()?</H3><P> - -Normally, transactions can not see the rows they modify. This allows <CODE> -UPDATE foo SET x = x + 1</CODE> to work correctly. -<P> - -However, there are cases where a transactions needs to see rows affected -in previous parts of the transaction. This is accomplished using a -Command Counter. Incrementing the counter allows transactions to be -broken into pieces so each piece can see rows modified by previous -pieces. <I>CommandCounterIncrement()</I> increments the Command -Counter, creating a new part of the transaction. <P> - -</BODY> + You must not directly change <I>live</I> tuples in this way. The + best way is to use <I>heap_modifytuple()</I> and pass it your + original tuple, and the values you want changed. It returns a + palloc'ed tuple, which you pass to <I>heap_replace().</I> You can + delete tuples by passing the tuple's <I>t_self</I> to + <I>heap_destroy().</I> You use <I>t_self</I> for + <I>heap_update()</I> too. Remember, tuples can be either system + cache copies, which may go away after you call + <I>ReleaseSysCache()</I>, or read directly from disk buffers, which + go away when you <I>heap_getnext()</I>, <I>heap_endscan</I>, or + <I>ReleaseBuffer()</I>, in the <I>heap_fetch()</I> case. Or it may + be a palloc'ed tuple, that you must <I>pfree()</I> when finished. + + <H3><A name="10">10</A>) What is elog()?</H3> + + <P><I>elog()</I> is used to send messages to the front-end, and + optionally terminate the current query being processed. The first + parameter is an elog level of <I>NOTICE,</I> <I>DEBUG,</I> + <I>ERROR,</I> or <I>FATAL.</I> <I>NOTICE</I> prints on the user's + terminal and the postmaster logs. <I>DEBUG</I> prints only in the + postmaster logs. <I>ERROR</I> prints in both places, and terminates + the current query, never returning from the call. <I>FATAL</I> + terminates the backend process. The remaining parameters of + <I>elog</I> are a <I>printf</I>-style set of parameters to + print.</P> + + <H3><A name="11">11</A>) What is configure all about?</H3> + + <P>The files <I>configure</I> and <I>configure.in</I> are part of + the GNU <I>autoconf</I> package. Configure allows us to test for + various capabilities of the OS, and to set variables that can then + be tested in C programs and Makefiles. Autoconf is installed on the + PostgreSQL main server. To add options to configure, edit + <I>configure.in,</I> and then run <I>autoconf</I> to generate + <I>configure.</I></P> + + <P>When <I>configure</I> is run by the user, it tests various OS + capabilities, stores those in <I>config.status</I> and + <I>config.cache,</I> and modifies a list of <I>*.in</I> files. For + example, if there exists a <I>Makefile.in,</I> configure generates + a <I>Makefile</I> that contains substitutions for all @var@ + parameters found by configure.</P> + + <P>When you need to edit files, make sure you don't waste time + modifying files generated by <I>configure.</I> Edit the <I>*.in</I> + file, and re-run <I>configure</I> to recreate the needed file. If + you run <I>make distclean</I> from the top-level source directory, + all files derived by configure are removed, so you see only the + file contained in the source distribution.</P> + + <H3><A name="12">12</A>) How do I add a new port?</H3> + + <P>There are a variety of places that need to be modified to add a + new port. First, start in the <I>src/template</I> directory. Add an + appropriate entry for your OS. Also, use <I>src/config.guess</I> to + add your OS to <I>src/template/.similar.</I> You shouldn't match + the OS version exactly. The <I>configure</I> test will look for an + exact OS version number, and if not found, find a match without + version number. Edit <I>src/configure.in</I> to add your new OS. + (See configure item above.) You will need to run autoconf, or patch + <I>src/configure</I> too.</P> + + <P>Then, check <I>src/include/port</I> and add your new OS file, + with appropriate values. Hopefully, there is already locking code + in <I>src/include/storage/s_lock.h</I> for your CPU. There is also + a <I>src/makefiles</I> directory for port-specific Makefile + handling. There is a <I>backend/port</I> directory if you need + special files for your OS.</P> + + <H3><A name="13">13</A>) What is CommandCounterIncrement()?</H3> + + <P>Normally, transactions can not see the rows they modify. This + allows <CODE>UPDATE foo SET x = x + 1</CODE> to work correctly.</P> + + <P>However, there are cases where a transactions needs to see rows + affected in previous parts of the transaction. This is accomplished + using a Command Counter. Incrementing the counter allows + transactions to be broken into pieces so each piece can see rows + modified by previous pieces. <I>CommandCounterIncrement()</I> + increments the Command Counter, creating a new part of the + transaction.</P> + + <H3><A name="14">14</A>) Why don't we use threads in the + backend?</H3> + + <P>There are several reasons threads are not used:</P> + + <UL> + <LI>Historically, threads were unsupported and buggy.</LI> + + <LI>An error in one backend can corrupt other backends.</LI> + + <LI>Speed improvements using threads are small compared to the + remaining backend startup time.</LI> + + <LI>The backend code would be more complex.</LI> + </UL> + </BODY> </HTML> + |